# Explain how gas exchange occurs in an insect, referring to the structures involved and the process by which gases move.

> AQA A-Level Biology (7402) — 3.3.2 Gas Exchange · Explain · 5 marks

## Mark scheme (5 marks)

1. Insects have small openings called spiracles on the surface of their body
2. Air moves through spiracles into a network of tubes called tracheae (tracheal tubes)
3. Tracheae branch into smaller tubes called tracheoles which reach individual cells/tissues
4. Oxygen diffuses from the tracheoles into the cells (and carbon dioxide diffuses out of cells into tracheoles)
5. A large surface area / thin walls of tracheoles / moist lining maintains a steep concentration gradient / allows efficient diffusion

## Related

- [Revision notes for AQA A-Level Biology (7402)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-gas-exchange-occurs-in-34d04fa8) · Published by Druglandscape Ltd.